Thermal Convection Of Fluid Research Articles

Hydrothermal fluid alteration of the Ordovician epigenetic karstification reservoir in the Tahe Oilfield, Tarim Basin, NW China

In recent years, the Ordovician carbonate reservoirs in the Tarim Basin have received attention due to continuous advancements in of deep strata exploration for oil and gas. The Ordovician carbonates in the Tahe Oilfield have experienced multiple phases of tectonic movement and ancient karst action to form reservoirs consisting of multi-scale spaces such as large caves, fractures, and dissolution pores. This study identifies indicators of atmospheric freshwater karst and hydrothermal karst in the Ordovician carbonate rocks of the Tahe Oilfield by comparing and analyzing lithological observation, geochemical data, fluid inclusions, logging interpretation, and seismic data. The spatial and temporal distribution of karst reservoirs are summarized, and the results show that the stage of tectonic movement and pulsating uplift of strata occurred in the early Caledonian and Hercynian orogenies, and the carbonate rocks were uplifted to the surface and large-scale atmospheric freshwater karstification.In the deeper strata, the thermal convection of fluids caused by volcanic activity accelerated the thermochemical sulfate reduction (TSR), and the generated H2S gas accompanied the upward transport of hydrothermal fluids, which further dissolved and modified the original karst system, increasing the storage space. However, away from the heat source, calcite (positive Eu anomaly, higher 87Sr/86Sr ratio, lower δ18O value,) reprecipitated due to the temperature reduction, so the role of hydrothermal activity in reservoir reconstruction is limited. The two karst action patterns indicated that epigenetic karstification is an important process for forming carbonate reservoirs in the Tahe Oilfield and the basis of hydrothermal karst reservoir formation. This study demonstrates the research and exploration value of karstification for the geo-energy field, which could benefit sustainable development in the Tarim Basin.

Ferromagnetic Chaos in thermal convection of fluid through fractal–fractional differentiations

Ferromagnetic Chaos in thermal convection of fluid through fractal–fractional differentiations

Enhanced heat transport in thermal convection with suspensions of rod-like expandable particles

Thermal convection of fluid is a more efficient way than diffusion to carry heat from hot sources to cold places. Here, we experimentally study the Rayleigh–Bénard convection of aqueous glycerol solution in a cubic cell with suspensions of rod-like particles made of polydimethylsiloxane. The particles are inertial due to their large thermal expansion coefficient and finite sizes. The thermal expansion coefficient of the particles is three times larger than that of the background fluid. This contrast makes the suspended particles lighter than the local fluid in hot regions and heavier in cold regions. The heat transport is enhanced at relatively large Rayleigh number ( $\textit {Ra}$ ) but reduced at small $\textit {Ra}$ . We demonstrate that the increase of Nusselt number arises from the particle–boundary layer interactions: the particles act as ‘active’ mixers of the flow and temperature fields across the boundary layers.

Mineral System of the Streltsovka Caldera Uranium Deposits (East Transbaikalia)

Abstract—Various hypotheses, including alternative ones, have been put forward in the literature about the sources of ore substance and ore-forming fluids in the deposits of the Streltsovka ore field, which hosts the world’s largest uranium reserves, in excess of 250 000 t U: (1) uranium transport by ascending flow of ore-forming fluids that have separated from a deep subcrustal or intracrustal uranium-bearing felsic magma chamber and (2) uranium mobilization from uranium-bearing rocks of the volcano-tectonic structure of the Streltsovka caldera via postvolcanic thermoconvective circulation of the ore-forming fluids. For both hypotheses, the authors previously developed computer models of the paleohydronamic formation conditions of the largest in the ore field Antei–Streltsovka deposit, which presumed different uranium transport mechanisms with forced and free thermal convection of fluids, respectively. Both models yielded calculation results consistent with data on the reserves and formation temperatures of the Antei–Streltsovka ores. However, since the computer models are a simplified image of ore-forming systems, such agreement between the modeling results and a natural prototype only indicate the possibility of the proposed hypotheses on the formation conditions of the deposits. To solve the problem of their reality, additional information is necessary. Therefore, the authors of this paper have attempted a comparative analysis of the proposed alternative interpretations of the formation of the Antei–Streltsovka deposit using a methodology elaborated within the mineral systems concept. The results of our analysis substantiate the idea of successive forms of uranium transport by magmatic melt and ore-forming fluid to the mineral system of the Streltsovka ore field. The deep magmatic source was a feeder chamber for uranium transport by magmatic melts to the upper horizons of the crust with the formation of uranium-bearing rocks of the subvolcanic chamber and volcanic eruptions of the Streltsovka caldera. After uranium transport via magmatic melts, its subsequent redistribution occurred in the paleohydrothermal system with free thermal convection of fluids in the residual temperature field of the Streltsovka subvolcanic chamber. In this case, in the thermoconvective fluid circulation loop, conjugate processes of uranium mobilization could have taken place: (1) from the consolidated subvolcanic chamber, (2) from granitoid rocks of the caldera’s basement, and (3) from igneous felsic rocks in the caldera’s volcano-sedimentary cover. The coparticipation of these three potentially highly productive uranium sources in the ore mineralization process explains the origin of the unique uranium ore reserves of the Streltsovka ore field deposits.

Thermal Convection of Fluids as a Possible Mechanism for the Formation of the Unique Streltsovka and Antei Uranium Deposits (Eastern Transbaikalia)

The hydrothermal molybdenum–uranium deposits of the Streltsovka ore field are localized in a volcanic caldera of Late Mesozoic age. The paper presents the results of numerical modeling of free thermal convection of fluids in the residual thermal field of the consolidated magma chamber of the Streltsovka caldera, which justifies the idea of thermoconvective mechanism for the formation of the structurally conjugate Streltsovka and Antei deposits. The process of fluid heat and mass transfer in the Antei–Streltsovka oreforming system self-organized into a convection cell with a fluid circulation circuit including a descending convection branch along the ring-fault zone of the caldera, a lateral flow branch from the descending to the ascending convection branch in the caldera’s basement rocks, an ascending convection branch along faults of the Antei deposit, and a lateral return branch from the ascending to the descending convection branch along the caldera’s volcano-sedimentary rock fill, in which the ores of the Streltsovka deposit are localized. At the same time, formation of the total reserves of the Antei–Streltsovka deposit, largest in this ore field, was facilitated by uranium sourced, during the hydrothermal ore-forming process, not only from the uranium-rich rocks of the consolidated magma chamber, but also from the granitic host rocks of the Streltsovka caldera basement.

Henri Bénard: Thermal convection and vortex shedding

We present in this article the work of Henri Bénard (1874–1939), a French physicist who began the systematic experimental study of two hydrodynamic systems: the thermal convection of fluids heated from below (the Rayleigh–Bénard convection and the Bénard–Marangoni convection) and the periodical vortex shedding behind a bluff body in a flow (the Bénard–Kármán vortex street). Across his scientific biography, we review the interplay between experiments and theory in these two major subjects of fluid mechanics.

The role of the thermal convection of fluids in the formation of unconformity-type uranium deposits: the Athabasca Basin, Canada

In the global production of uranium, ~18% belong to the unconformity-type Canadian deposits localized in the Athabasca Basin. These deposits, which are unique in terms of their ore quality, were primarily studied by Canadian and French scientists. They have elaborated the diagenetic–hydrothermal hypothesis of ore formation, which suggests that (1) the deposits were formed within a sedimentary basin near an unconformity surface dividing the folded Archean–Proterozoic metamorphic basement and a gently dipping sedimentary cover, which is not affected by metamorphism; (2) the spatial accommodation of the deposits is controlled by the rejuvenated faults in the basement at their exit into the overlying sedimentary sequence; the ore bodies are localized above and below the unconformity surface; (3) the occurrence of graphite-bearing rocks is an important factor in controlling the local structural mineralization; (4) the ore bodies are the products of uranium precipitation on a reducing barrier. The mechanism that drives the circulation of ore-forming hydrothermal solutions has remained one of the main unclear questions in the general genetic concept. The ore was deposited above the surface of the unconformity due to the upflow discharge of the solution from the fault zones into the overlying conglomerate and sandstone. The ore formation below this surface is a result of the downflow migration of the solutions along the fault zones from sandstone into the basement rocks. A thermal convective system with the conjugated convection cells in the basement and sedimentary fill of the basin may be a possible explanation of why the hydrotherms circulate in the opposite directions. The results of our computations in the model setting of the free thermal convection of fluids are consistent with the conceptual reasoning about the conditions of the formation of unique uranium deposits in the Athabasca Basin. The calculated rates of the focused solution circulation through the fault zones in the upflow and downflow branches of a convection cell allow us to evaluate the time of ore formation up to the first hundreds of thousands years.

Possible role of fluids free thermal convection processes in formation of uranium deposits in the Streltsovska ore field (Eastern Trans-Baikal Region)

This paper reports the preliminary results of computer simulation of the free thermal convection of fluids in a residual thermal field of a consolidated shallow magma chamber related to caldera formation. The deeply penetrating thermoconvective circulation of fluids provided conditions for mobilization and transportation of uranium from the vast area under the caldera to the ore deposition sites.

Linked thermal convection of the basement and basinal fluids in formation of the unconformity‐related uranium deposits in the Athabasca Basin, Saskatchewan, Canada

AbstractWorld‐class unconformity‐related U deposits in the Athabasca Basin (Saskatchewan, Canada) are generally located within or near fault zones that intersect the unconformity between the Athabasca Group sedimentary basin rocks and underlying metamorphic basement rocks. Two distinct subtypes of unconformity‐related uranium deposits have been identified: those hosted primarily in the Athabasca Group sandstones (sediment‐hosted) and those hosted primarily in the underlying basement rocks (basement‐hosted). Although significant research on these deposits has been carried out, certain aspects of their formation are still under discussion, one of the main issues being the fluid flow mechanisms responsible for uranium mineralization. The intriguing feature of this problem is that sediment‐hosted and basement‐hosted deposits are characterized by oppositely directed vectors of fluid flow via associated fault zones. Sediment‐hosted deposits formed via upward flow of basement fluids, basement‐hosted deposits via downward flow of basinal fluids. We have hypothesized that such flow patterns are indicative of the fluid flow self‐organization in fault‐bounded thermal convection (Transport in Porous Media, 110, 2015, 25). To explore this hypothesis, we constructed a simplified hydrogeologic model with fault‐bounded thermal convection of fluids in the faulted basement linked with fluid circulation in the overlying fault‐free sandstone horizon. Based on this model, a series of numerical experiments was carried out to simulate the hypothesized fluid flow patterns. The results obtained are in reasonable agreement with the concept of fault‐bounded convection cells as an explanation of focused upflow and downflow across the basement/sandstone unconformity. We then discuss application of the model to another debated problem, the uranium source for the ore‐forming basinal brines.

Onset of Fault-Bounded Free Thermal Convection in a Fluid-Saturated Horizontal Permeable Porous Layer

Development of free thermal convection of fluids in permeable rock domain with two parallel vertical faults is considered. Permeability of the faults is much higher than in the enclosing rocks. Upper and lower boundaries of the rock domain are horizontal. The lower boundary of the domain is impermeable. The upper boundary is open. Temperatures at these boundaries are fixed, and the temperature at the lower boundary is higher than the upper one. Three-dimensional model is considered. The conditions for thermal convection onset were obtained by linear stability analysis. The boundary condition for the convection onset is defined as existence of a steady-state solution of the governing equations for the fluid flow and heat transfer with nonzero convection velocities. This takes place when Rayleigh number exceeds certain critical value. These critical Rayleigh numbers are determined for different values of permeability contrast between the faults and the enclosing rocks and different distances between the faults. It is shown that thermal convection in the considered system can develop at Rayleigh numbers which are lower than the critical value for homogeneous rocks. Influence of Rayleigh number on convection cell pattern is analyzed. The role of the thermal convection in the considered systems in formation of ore deposits is examined.

Vibrational convection of heat-generating fluid in a rotating horizontal cylinder. The role of relative cavity length

Thermal convection of fluid with internal heat sources in a rotating horizontal cylinder with isothermal boundary and adiabatic ends is investigated experimentally. Under the action of gravity nonisothermal liquid oscillates in the cavity frame. These tidal oscillations generate the average mass force and, as a result, excite convection. The steady convection developing by this mechanism is called thermal vibrational. Centrifugal force in the considered case plays a stabilizing role. The objects of studying are the excitation thresholds of the averaged convection, heat transfer and the structure of convective flows. The parameters varying in the experiments are heat release rate, relative length of the cylinder and rotation velocity. It is found that the inertial waves which are generated near the ends of the cavity by tidal oscillations of nonisothermal liquid effect the convection. The intensity of flows excited by these waves is relatively low, but significant especially below the threshold of thermal vibrational convection. It is shown that the influence of inertial waves on heat transfer and structure of convective flows strongly depends on the cavity aspect ratio.

Boundary Observer for Output-Feedback Stabilization of Thermal-Fluid Convection Loop

In this paper, we consider a 2-D model of thermal fluid convection that exhibits the prototypical Rayleigh-Bernard convective instability. The fluid is enclosed between two cylinders, heated from above, and cooled from below, which makes its motion unstable for a large enough Rayleigh number. We design an stabilizing output feedback boundary control law for a realistic collocated setup, with actuation and measurements located at the outer boundary. Actuation is through rotation (direct velocity actuation) and heat flux (heating or cooling) of the outer cylinder, while measurements of friction and temperature are obtained at the same boundary. Though only a linearized version of the plant is considered in the design, an extensive closed loop simulation study of the nonlinear model shows that our design works for reasonably large initial conditions. A highly accurate approximation to the control kernels and observer output injection gains is found in closed form.

Convective stability of a nonisothermal fluid in a rotating horizontal coaxial gap

The thermal fluid convection in a coaxial horizontal gap uniformly rotating about its axis is investigated. The threshold above which convective flows are excited and the structure of these flows are studied. It is found that convection ensues irrespective of whether the inner or outer boundary temperature is higher. Convection manifests itself in the threshold development of rolls elongated in the direction of the rotation axis and is determined by two different mechanisms. If the layer is heated from outside, the centrifugal convection mechanism plays a leading part and the diameter of the convective rolls is comparable with the layer thickness. If the higher is the temperature of the inner boundary of the layer, the centrifugal inertia force has a stabilizing effect and convection development is related with the action of thermal vibrational mechanism. The latter is determined by gravity-generated oscillations of the nonisothermal fluid relative to the cavity. The wave number of the vibrational convective structures is several times smaller than under centrifugal convection. The results obtained broaden our understanding of thermal convection in systems rotating in external static force fields.

Large-scale thermal convection in a horizontal porous layer

In a range of physical systems, the first instability in Rayleigh-Bérnard convection between nearly thermally insulating horizontal plates is large scale. This holds for thermal convection of fluids saturating porous media. Large-scale thermal convection in a horizontal layer is governed by remarkably similar equations both in the presence of a porous matrix and without it, with only one additional term for the latter case, which, however, vanishes under certain conditions (e.g., two-dimensional flows or infinite Prandtl number). We provide a rigorous derivation of long-wavelength equations for a porous layer with inhomogeneous heating and possible pumping.

A New Method for Measuring Flow Velocity Using Periodic Heating and the Sensing Characteristics of a Micro Flow Sensor Manufactured by MEMS Technique

In this paper, a new method for measuring flow velocity has been proposed. It adopts periodic heating as an input signal, and flow velocity is deduced from the phase delay of output signal, coming from adjacent temperature sensors. Since this method doesn't use absolute values of the temperature, but only phase delay, it has a strong robustness against possible noise. We have developed a simplified model based on a quasi-steady state of thermal convection in fluid, and compared the model predictions with experimental results. It's found that the model is able to explain the experimental results qualitatively. The proposed method, which makes use of a micro sensor manufactured by MEMS technique, provides a wide dynamic-range of flow velocity measurements with a simple electronic circuit.

Fluid convection observed from temperature logs in the karst formation of the Yucatán Peninsula, Mexico

Temperature?depth profiles, obtained during three campaigns of temperature logging in boreholes of the Yucat?n Peninsula in the period 2002?2004, display the effects of thermal fluid convection. These effects are most pronounced in the uppermost part of the 1.5 km deep borehole Yaxcopoil-1 drilled within the Chicxulub impact crater. The convective zone is clearly discernible in all three profiles measured here in March 2002, May 2003 and February 2004. The loggings have revealed a gradual downward propagation of the convective features from the uppermost 145 m of the temperature profile to 230 m between the first and second loggings (with a propagation rate of 6 m/month) and to 265 m between the second and third loggings (4 m/month). A signature of the fluid convection is also evident in all other temperature logs in the area measured during the 2003 campaign, namely in four UNAM boreholes 2, 5, 7 and 8, three hydrogeological boreholes 1A, 1B and 1C, in a borehole at the meteorological observatory M?rida and in the cenote Ucil. The fresh/salt water interface is clearly visible in most of the logs as a zone of increased temperature gradient. The varying intensity of the convective features among the individual logs seems to be correlated with the borehole position relative to the impact structure.

Nonlinear analysis for the cooling effect of Qinghai-Tibetan railway embankment with different structures in permafrost regions

The thermal convection of fluid inside ballast layer and ripped-rock layer, which are regarded as porous media in railway embankment, is the process of heat and mass transfer. In this paper, in order to research the influence of different embankment structures and geometries on the underlying permafrost thermal regime along Qinghai-Tibetan Railway, a numerical representation of the unsteady two-dimensional continuity, momentum (non-Darcy) and energy equations of thermal convection for incompressible fluid in porous media is used to analyze temperature characteristics of a traditional ballast embankment, a horizontal ripped-rock embankment and two U-shaped ripped-rock embankments for the 50 years. The calculated results indicate: (1) the traditional ballast embankment will cause the great degradation of the underlying permafrost under the assumption that the air temperature will warm up 2.6 °C in the 50 years; (2) the U-shaped ripped-rock embankment with 150-cm-thick ripped-rock layer and 160-cm-wide ripped-rock revetment can efficiently protect the underlying permafrost. However, 120-cm-thick horizontal ripped-rock layer has weak cooling effect. Therefore, the horizontal ripped-rock layer thickness is a very important factor to the effect of ripped-rock embankment. These analyses indicate that reasonable ripped-rock embankment structure and embankment geometry can provide an effective mechanism for preserving permafrost under trend of global warming and avoiding large deformation and embankment failure due to thaw settlement in high-temperature permafrost regions along Qinghai-Tibetan Railway.

Thermal convection in a ferrofluid supported by thermodiffusion

Convective motion has been investigated in a ferrofluid layer heated from below. In contrast to normal experiments on thermal convection in fluids, the focus of this investigation was devoted to the destabilizing effect of the density redistribution in the fluid forced by thermal diffusion of the magnetic particles relative to the carrier liquid. It could be shown that the fluid layer is destabilized at a temperature difference well below the critical limit for a one-component fluid. It was found that the convective flow is stable in time and the measured convection amplitude could be fitted with a theory given by Hollinger et al. (Phys. Rev. E 57 (1997) 4).

Engineering Applications of Noncommutative Harmonic Analysis: With Emphasis on Rotation and Motion Groups

<i>Engineering Applications of Noncommutative Harmonic Analysis: With Emphasis on Rotation and Motion Groups</i>

Characterization of the stationary states of a dilute vibrofluidized granular bed.

This paper reports two phenomena in an event driven simulation of a dilute vibrofluidized granular material in two dimensions. Both phenomena show inhomogeneity in the horizontal direction. They are convection rolls similar to the Rayleigh-Bénard thermal convection in fluids, and a clustering instability, where the bed spontaneously phase separates into coexisting dense and dilute regions. Detailed investigations show that these are different from the known instabilities in a vibrated granular medium. Characterization of these instabilities is carried out with a phase diagram using suitable parameters from the kinetic theory of vibrofluidized beds.